The present invention pertains to a sputtering target having a complex three-dimensional (stereoscopic) structure formed by die forging, and the manufacturing method thereof.
In recent years, the sputtering method for forming a film from materials such as metal or ceramics has been used in numerous fields such as electronics, corrosion resistant materials and ornaments, catalysts, as well as in the manufacture of cutting/grinding materials and abrasion resistant materials.
Although the sputtering method itself is a well-known method in the foregoing fields, recently, particularly in the electronics field, a sputtering target suitable for forming films of complex shapes and forming circuits is in demand. For instance, a target having a three-dimensional (stereoscopic) structure in which the cross section is of a hat shape or dome shape, or a combination thereof is now being used.
Generally, a target having this kind of three-dimensional structure is manufactured by performing hot forging to an ingot or billet formed by dissolving and casting metal, thereafter performing annealing thereto, and further performing die forging thereto. In this kind of manufacturing procedure, the hot forging performed to the ingot or billet will destroy the cast structure, disperse or eliminate the pores and segregations, and, by further annealing this, recrystallization will occur, and the precision and strength of the structure can be improved to a certain degree.
Next, this forged, recrystallized and annealed material is formed into a target shape having a prescribed three-dimensional structure via die forging, and, thereafter, recrystallization annealing and straightening annealing are performed thereto and surface treatment is ultimately performed thereto in order to manufacture the target.
With this type of target manufacturing method, although there is no particular problem upon manufacturing an ordinary flat target, with a target having a three-dimensional (stereoscopic) structure in which the cross section is of a hat shape or dome shape, or the combination thereof, since there are portions that will be strongly subject to plastic deformation and portions that will hardly be subject to plastic deformation during die forging, there are cases where abnormal differences occur in the size of the crystal grains during the recrystallization annealing and straightening annealing thereafter.
For instance, although portions facing the forging direction will merely be subject to compressive force, portions along the forging direction; that is, the sidewall of the three-dimensional structure will be subject to harsh, strong processing.
As described above, the grain size of the recrystallized grains upon annealing will significantly differ at portions that are strongly subject to plastic deformation and portions that are weakly subject to plastic deformation. In other words, crystals become fine grains at portions that are strongly subject to plastic deformation, and crystals become coarse grains at portions that are weakly subject to plastic deformation. Further, the boundary area of such portions that are strongly and weakly subject to plastic deformation will become a crystal structure in which the fine grains and coarse grains exist at random, or in which the fine grains and coarse grains change in a phased manner.
Generally, upon performing sputtering, the finer the crystals of the target, the more even the deposition, and a film having even and stable characteristics, with few generation of arcing or particles, can be obtained.
Therefore, the existence of the foregoing coarse crystal grains and irregular crystal grains that generate during die forging or the annealing to be performed thereafter will increase the generation of arcing and particles, and there is a significant problem in that the quality of the sputtering film will deteriorate. Needless to say, it is not possible to consider using a stamp-forged product in which strain remains therein, and this will further deteriorate the quality.
In light of the above, there is a problem in that a sputtering target having a three-dimensional structure manufactured by die forging would deteriorate the film property pursuant to the crystal grains becoming coarse and uneven.